可调谐二极管激光吸收光谱(TDLAS)技术是利用二极管激光器波长调谐特性,获得被测气体在特征吸收光谱范围内的吸收光谱,从而对污染气体进行定性或定量分析。通过该方法对环境空气中甲烷(CH4)的含量进行了长时间的监测。以室温下工作的近红外可调谐半导体激光器作为光源；使用多次反射池增加吸收光程来提高检测灵敏度；并且使用了二次谐波检测技术进一步降低了检测限,使检测限低于0.087 mg/m3,满足了对环境空气中甲烷进行监测的需要。

Tunable diode laser absorption spectroscopy (TDLAS) technique is a new method to detect trace-gas qualitatively or quantificationally based on the scan characteristic of the diode laser to obtain the absorption spectra in the characteristic absorption region. It needs to combine with a long absorption path in the ambient trace-gas measurements. It has a significant advantage not only in sensitivity but also in rapidity of response. The experimental results of monitoring of methane of the ambient air in a long time with a ground-based portable TDLAS system are described; it works with a room-temperature near infrared tunable diode laser to measure methane in the ambient air, the path length is lengthened by the multiple-reflection cell to lower the detection limit; and the second harmonic detection is used to lower the detection limit farther; the detection limit is below 0.087 mg/m3, that is enough to the monitoring of ambient methane.